Mechanism and preclinical prevention of increased breast cancer risk caused by pregnancy

Dual role of pregnancy in breast cancer risk

Reproductive history is one of the strongest risk factors for breast cancer in women. Pregnancy can promote short-term breast cancer risk, but also reduce a woman's lifetime risk of breast cancer. Changes in hormone levels before and after pregnancy are one of the key factors in breast cancer risk. This article summarizes the changes in hormone levels before and after pregnancy, and the roles of hormones in mammary gland development and breast cancer progression. Other factors, such as changes in breast morphology and mammary gland differentiation, changes in the proportion of mammary stem cells (MaSCs), changes in the immune and inflammatory environment, and changes in lactation before and after pregnancy, also play key roles in the occurrence and development of breast cancer. This review discusses the dual effects and the potential mechanisms of pregnancy on breast cancer risk from the above aspects, which is helpful to understand the complexity of female breast cancer occurrence.

Status of breast cancer detection in young women and potential of liquid biopsy

Young onset breast cancer (YOBC) is an increasing demographic with unique biology, limited screening, and poor outcomes. Further, women with postpartum breast cancers (PPBCs), cancers occurring up to 10 years after childbirth, have worse outcomes than other young breast cancer patients matched for tumor stage and subtype. Early-stage detection of YOBC is critical for improving outcomes. However, most young women (under 45) do not meet current age guidelines for routine mammographic screening and are thus an underserved population. Other challenges to early detection in this population include reduced performance of standard of care mammography and reduced awareness. Women often face significant barriers in accessing health care during the postpartum period and disadvantaged communities face compounding barriers due to systemic health care inequities. Blood tests and liquid biopsies targeting early detection may provide an attractive option to help address these challenges. Test development in this area includes understanding of the unique biology involved in YOBC and in particular PPBCs that tend to be more aggressive and deadly. In this review, we will present the status of breast cancer screening and detection in young women, provide a summary of some unique biological features of YOBC, and discuss the potential for blood tests and liquid biopsy platforms to address current shortcomings in timely, equitable detection.

Advances in Immunocompetent Mouse and Rat Models

Rodent models of breast cancer have played critical roles in our understanding of breast cancer development and progression as well as preclinical testing of cancer prevention and therapeutics. In this article, we first review the values and challenges of conventional genetically engineered mouse (GEM) models and newer iterations of these models, especially those with inducible or conditional regulation of oncogenes and tumor suppressors. Then, we discuss nongermline (somatic) GEM models of breast cancer with temporospatial control, made possible by intraductal injection of viral vectors to deliver oncogenes or to manipulate the genome of mammary epithelial cells. Next, we introduce the latest development in precision editing of endogenous genes using in vivo CRISPR-Cas9 technology. We conclude with the recent development in generating somatic rat models for modeling estrogen receptor-positive breast cancer, something that has been difficult to accomplish in mice.

Cabergoline as a Novel Strategy for Post-Pregnancy Breast Cancer Prevention in Mice and Human

Post-pregnancy breast cancer often carries a poor prognosis, posing a major clinical challenge. The increasing trend of later-life pregnancies exacerbates this risk, highlighting the need for effective chemoprevention strategies. Current options, limited to selective estrogen receptor modulators, aromatase inhibitors, or surgical procedures, offer limited efficacy and considerable side effects. Here, we report that cabergoline, a dopaminergic agonist, reduces the risk of breast cancer post-pregnancy in a Brca1/P53-deficient mouse model, with implications for human breast cancer prevention. We show that a single dose of cabergoline administered post-pregnancy significantly delayed the onset and reduced the incidence of breast cancer in Brca1/P53-deficient mice. Histological analysis revealed a notable acceleration in post-lactational involution over the short term, characterized by increased apoptosis and altered gene expression related to ion transport. Over the long term, histological changes in the mammary gland included a reduction in the ductal component, decreased epithelial proliferation, and a lower presence of recombinant Brca1/P53 target cells, which are precursors of tumors. These changes serve as indicators of reduced breast cancer susceptibility. Additionally, RNA sequencing identified gene expression alterations associated with decreased proliferation and mammary gland branching. Our findings highlight a mechanism wherein cabergoline enhances the protective effect of pregnancy against breast cancer by potentiating postlactational involution. Notably, a retrospective cohort study in women demonstrated a markedly lower incidence of post-pregnancy breast cancer in those treated with cabergoline compared to a control group. Our work underscores the importance of enhancing postlactational involution as a strategy for breast cancer prevention, and identifies cabergoline as a promising, low-risk option in breast cancer chemoprevention. This strategy has the potential to revolutionize breast cancer prevention approaches, particularly for women at increased risk due to genetic factors or delayed childbirth, and has wider implications beyond hereditary breast cancer cases.

The mutational landscape of the adult healthy parous and nulliparous human breast

The accumulation of somatic mutations in healthy human tissues has been extensively characterized, but the mutational landscape of the healthy breast is still poorly understood. Our analysis of whole-genome sequencing shows that in line with other healthy organs, the healthy breast during the reproduction years accumulates mutations with age, with the rate of accumulation in the epithelium of 15.24 ± 5 mutations/year. Both epithelial and stromal compartments contain mutations in breast-specific driver genes, indicative of subsequent positive selection. Parity- and age-associated differences are evident in the mammary epithelium, partly explaining the observed difference in breast cancer risk amongst women of different childbearing age. Parity is associated with an age-dependent increase in the clone size of mutated epithelial cells, suggesting that older first-time mothers have a higher probability of accumulating oncogenic events in the epithelium compared to younger mothers or nulliparous women. In conclusion, we describe the reference genome of the healthy female human breast during reproductive years and provide evidence of how parity affects the genomic landscape of the mammary gland.

Gestational Breast Cancer - a Review of Outcomes, Pathophysiology, and Model Systems

The onset of pregnancy marks the start of offspring development, and represents the key physiological event that induces re-organization and specialization of breast tissue. Such drastic tissue remodeling has also been linked to epithelial cell transformation and the establishment of breast cancer (BC). While patient outcomes for BC overall continue to improve across subtypes, prognosis remains dismal for patients with gestational breast cancer (GBC) and post-partum breast cancer (PPBC), as pregnancy and lactation pose additional complications and barriers to several gold standard clinical approaches. Moreover, delayed diagnosis and treatment, coupled with the aggressive time-scale in which GBC metastasizes, inevitably contributes to the higher incidence of disease recurrence and patient mortality. Therefore, there is an urgent and evident need to better understand the factors contributing to the establishment and spreading of BC during pregnancy. In this review, we provide a literature-based overview of the diagnostics and treatments available to patients with BC more broadly, and highlight the treatment deficit patients face due to gestational status. Further, we review the current understanding of the molecular and cellular mechanisms driving GBC, and discuss recent advances in model systems that may support the identification of targetable approaches to block BC development and dissemination during pregnancy. Our goal is to provide an updated perspective on GBC, and to inform critical areas needing further exploration to improve disease outcome.

In Vivo Gene Delivery into Mouse Mammary Epithelial Cells Through Mammary Intraductal Injection

Mouse mammary glands comprise ductal trees, which are lined by epithelial cells and have one opening at the tip of each nipple. The epithelial cells play a major role in mammary gland function and are the origin of most mammary tumors. Introducing genes of interest into mouse mammary epithelial cells is a critical step in evaluating gene function in epithelial cells and generating mouse mammary tumor models. This goal can be accomplished through the intraductal injection of a viral vector carrying the genes of interest into the mouse mammary ductal tree. The injected virus subsequently infects mammary epithelial cells, bringing in the genes of interest. The viral vector can be lentiviral, retroviral, adenoviral, or adenovirus-associated viral (AAV). This study demonstrates how a gene of interest is delivered into mammary epithelial cells through mouse mammary intraductal injection of a viral vector. A lentivirus carrying GFP is used to show stable expression of a delivered gene, and a retrovirus carrying Erbb2 (HER2/Neu) is used to demonstrate oncogene-induced atypical hyperplastic lesions and mammary tumors.

Short-term PI3K Inhibition Prevents Breast Cancer in Preclinical Models

Antiestrogen medication is the only chemoprevention currently available for women at a high risk of developing breast cancer; however, antiestrogen therapy requires years to achieve efficacy and has adverse side effects. Therefore, it is important to develop an efficacious chemoprevention strategy that requires only a short course of treatment. PIK3CA is commonly activated in breast atypical hyperplasia, the known precancerous precursor of breast cancer. Targeting PI3K signaling in these precancerous lesions may offer a new strategy for chemoprevention. Here, we first established a mouse model that mimics the progression from precancerous lesions to breast cancer. Next, we demonstrated that a short-course prophylactic treatment with the clinically approved PI3K inhibitor alpelisib slowed early lesion expansion and prevented cancer formation in this model. Furthermore, we showed that alpelisib suppressed ex vivo expansion of patient-derived atypical hyperplasia. Together, these data indicate that the progression of precancerous breast lesions heavily depends on the PI3K signaling, and that prophylactic targeting of PI3K activity can prevent breast cancer.

PREVENTION RELEVANCE

PI3K protein is abnormally high in breast precancerous lesions. This preclinical study demonstrates that the FDA-approved anti-PI3K inhibitor alpelisib can prevent breast cancer and thus warrant future clinical trials in high-risk women.

Esr1 but Not CYP19A1 Overexpression in Mammary Epithelial Cells during Reproductive Senescence Induces Pregnancy-Like Proliferative Mammary Disease Responsive to Anti-Hormonals

Molecular-level analyses of breast carcinogenesis benefit from vivo disease models. Estrogen receptor 1 (Esr1) and cytochrome P450 family 19 subfamily A member 1 (CYP19A1) overexpression targeted to mammary epithelial cells in genetically engineered mouse models induces largely similar rates of proliferative mammary disease in prereproductive senescent mice. Herein, with natural reproductive senescence, Esr1 overexpression compared with CYP19A1 overexpression resulted in significantly higher rates of preneoplasia and cancer. Before reproductive senescence, Esr1, but not CYP19A1, overexpressing mice are tamoxifen resistant. However, during reproductive senescence, Esr1 mice exhibited responsiveness. Both Esr1 and CYP19A1 are responsive to letrozole before and after reproductive senescence. Gene Set Enrichment Analyses of RNA-sequencing data sets showed that higher disease rates in Esr1 mice were accompanied by significantly higher expression of cell proliferation genes, including members of prognostic platforms for women with early-stage hormone receptor-positive disease. Tamoxifen and letrozole exposure induced down-regulation of these genes and resolved differences between the two models. Both Esr1 and CYP19A1 overexpression induced abnormal developmental patterns of pregnancy-like gene expression. This resolved with progression through reproductive senescence in CYP19A1 mice, but was more persistent in Esr1 mice, resolving only with tamoxifen and letrozole exposure. In summary, genetically engineered mouse models of Esr1 and CYP19A1 overexpression revealed a diversion of disease processes resulting from the two distinct molecular pathophysiological mammary gland-targeted intrusions into estrogen signaling during reproductive senescence.

STAT5 confers lactogenic properties in breast tumorigenesis and restricts metastatic potential

Signal transducer and activator of transcription 5 (STAT5) promotes cell survival and instigates breast tumor formation, and in the normal breast it also drives alveolar differentiation and lactogenesis. However, whether STAT5 drives a differentiated phenotype in breast tumorigenesis and therefore impacts cancer spread and metastasis is unclear. We found in two genetically engineered mouse models of breast cancer that constitutively activated Stat5a (Stat5a^ca) caused precancerous mammary epithelial cells to become lactogenic and evolve into tumors with diminished potential to metastasize. We also showed that STAT5a^ca reduced the migratory and invasive ability of human breast cancer cell lines in vitro. Furthermore, we demonstrated that STAT5a^ca overexpression in human breast cancer cells lowered their metastatic burden in xenografted mice. Moreover, RPPA, Western blotting, and studies of ChIPseq data identified several EMT drivers regulated by STAT5. In addition, bioinformatic studies detected a correlation between STAT5 activity and better prognosis of breast cancer patients. Together, we conclude that STAT5 activation during mammary tumorigenesis specifies a tumor phenotype of lactogenic differentiation, suppresses EMT, and diminishes potential for subsequent metastasis.

Serum hormone levels and normal breast histology among premenopausal women

PURPOSE

Breast terminal duct lobular units (TDLUs) are the main source of breast cancer (BC) precursors. Higher serum concentrations of hormones and growth factors have been linked to increased TDLU numbers and to elevated BC risk, with variable effects by menopausal status. We assessed associations of circulating factors with breast histology among premenopausal women using artificial intelligence (AI) and preliminarily tested whether parity modifies associations.

METHODS

Pathology AI analysis was performed on 316 digital images of H&E-stained sections of normal breast tissues from Komen Tissue Bank donors ages ≤ 45 years to assess 11 quantitative metrics. Associations of circulating factors with AI metrics were assessed using regression analyses, with inclusion of interaction terms to assess effect modification.

RESULTS

Higher prolactin levels were related to larger TDLU area (p < 0.001) and increased presence of adipose tissue proximate to TDLUs (p < 0.001), with less significant positive associations for acini counts (p = 0.012), dilated acini (p = 0.043), capillary area (p = 0.014), epithelial area (p = 0.007), and mononuclear cell counts (p = 0.017). Testosterone levels were associated with increased TDLU counts (p < 0.001), irrespective of parity, but associations differed by adipose tissue content. AI data for TDLU counts generally agreed with prior visual assessments.

CONCLUSION

Among premenopausal women, serum hormone levels linked to BC risk were also associated with quantitative features of normal breast tissue. These relationships were suggestively modified by parity status and tissue composition. We conclude that the microanatomic features of normal breast tissue may represent a marker of BC risk.

STAT5 is activated in macrophages by breast cancer cell-derived factors and regulates macrophage function in the tumor microenvironment

BACKGROUND

In breast cancer, complex interactions between tumor cells and cells within the surrounding stroma, such as macrophages, are critical for tumor growth, progression, and therapeutic response. Recent studies have highlighted the complex nature and heterogeneous populations of macrophages associated with both tumor-promoting and tumor-inhibiting phenotypes. Defining the pathways that drive macrophage function is important for understanding their complex phenotypes within the tumor microenvironment. Signal transducer and activator of transcription (STAT) transcription factors, such as STAT5, are key regulators of immune cell function. The studies described here investigate the functional contributions of STAT5 to tumor-associated macrophage function in breast cancer.

METHODS

Initial studies were performed using a panel of human breast cancer and mouse mammary tumor cell lines to determine the ability of tumor cell-derived factors to induce STAT5 activation in macrophages. Further studies used these models to identify soluble factors that activate STAT5 in macrophages. To delineate STAT5-specific contributions to macrophage function, a conditional model of myeloid STAT5 deletion was used for in vitro, RNA-sequencing, and in vivo studies. The effects of STAT5 deletion in macrophages on tumor cell migration and metastasis were evaluated using in vitro co-culture migration assays and an in vivo tumor cell-macrophage co-injection model.

RESULTS

We demonstrate here that STAT5 is robustly activated in macrophages by tumor cell-derived factors and that GM-CSF is a key cytokine stimulating this pathway. The analysis of RNA-seq studies reveals that STAT5 promotes expression of immune stimulatory genes in macrophages and that loss of STAT5 in macrophages results in increased expression of tissue remodeling factors. Finally, we demonstrate that loss of STAT5 in macrophages promotes tumor cell migration in vitro and mammary tumor metastasis in vivo.

CONCLUSIONS

Breast cancer cells produce soluble factors, such as GM-CSF, that activate the STAT5 pathway in macrophages and drive expression of inflammatory factors. STAT5 deletion in myeloid cells enhances metastasis, suggesting that STAT5 activation in tumor-associated macrophages protects against tumor progression. Understanding mechanisms that drive macrophage function in the tumor microenvironment will ultimately lead to new approaches that suppress tumor-promoting functions while enhancing their anti-tumor functions.

Targeting the Pro-Survival Protein BCL-2 to Prevent Breast Cancer

Current chemopreventive strategies require 3-5 years of continuous treatment and have the concerns of significant side effects; therefore, new chemopreventive agents that require shorter and safer treatments are urgently needed. In this study, we developed a new murine model of breast cancer that mimics human breast cancer initiation and is ideal for testing the efficacy of chemopreventive therapeutics. In this model, introduction of lentivirus carrying a PIK3CA gene mutant commonly found in breast cancers infects a small number of the mammary cells, leading to atypia first and then to ductal carcinomas that are positive for both estrogen receptor and progesterone receptor. Venetoclax is a BH3 mimetic that blocks the anti-apoptotic protein BCL-2 and has efficacy in treating breast cancer. We found that venetoclax treatment of atypia-bearing mice delayed the progression to tumors, improved overall survival, and reduced pulmonary metastasis. Therefore, prophylactic treatment to inhibit the pro-survival protein BCL-2 may provide an alternative to the currently available regimens in breast cancer prevention.

HER2 Activation and Endocrine Treatment Resistance in HER2-negative Breast Cancer

The lethality of estrogen receptor alpha positive (ER+) breast cancer, which is often considered to have better prognosis than other subtypes, is defined by resistance to the standard of care endocrine treatment. Relapse and metastasis are inevitable in almost every patient whose cancer is resistant to endocrine treatment. Therefore, understanding the underlying causes of treatment resistance remains an important biological and clinical focus of research in this area. Growth factor receptor pathway activation, specifically HER2 activation, has been identified as 1 mechanism of endocrine treatment resistance across a range of experimental model systems. However, clinical trials conducted to test whether targeting HER2 benefits patients with endocrine treatment-resistant ER+ breast cancer have consistently and disappointingly shown mixed results. One reason for the failure of these clinical trials could be the complexity of crosstalk between ER, HER2, and other growth factor receptors and the fluidity of HER2 activation in these cells, which makes it challenging to identify stratifiers for this targeted intervention. In the absence of stratifiers that can be assayed at diagnosis to allow prospective tailoring of HER2 inhibition to the right patients, clinical trials will continue to disappoint. To understand stratifiers, it is important that the field invests in key understudied areas of research including characterization of the tumor secretome and receptor activation in response to endocrine treatment, and mapping the ER-HER2 growth factor network in the normal and developing mammary gland. Understanding these mechanisms further is critical to improving outcomes for the hard-to-treat endocrine treatment-resistant ER+ breast cancer cohort.

Exposure to Propylparaben During Pregnancy and Lactation Induces Long-Term Alterations to the Mammary Gland in Mice

The mammary gland is a hormone sensitive organ that is susceptible to endocrine-disrupting chemicals (EDCs) during the vulnerable periods of parous reorganization (ie, pregnancy, lactation, and involution). Pregnancy is believed to have long-term protective effects against breast cancer development; however, it is unknown if EDCs can alter this effect. We examined the long-term effects of propylparaben, a common preservative used in personal care products and foods, with estrogenic properties, on the parous mouse mammary gland. Pregnant BALB/c mice were treated with 0, 20, 100, or 10 000 µg/kg/day propylparaben throughout pregnancy and lactation. Unexposed nulliparous females were also evaluated. Five weeks post-involution, mammary glands were collected and assessed for changes in histomorphology, hormone receptor expression, immune cell number, and gene expression. For several parameters of mammary gland morphology, propylparaben reduced the effects of parity. Propylparaben also increased proliferation, but not stem cell number, and induced modest alterations to expression of ERα-mediated genes. Finally, propylparaben altered the effect of parity on the number of several immune cell types in the mammary gland. These results suggest that propylparaben, at levels relevant to human exposure, can interfere with the effects of parity on the mouse mammary gland and induce long-term alterations to mammary gland structure. Future studies should address if propylparaben exposures negate the protective effects of pregnancy on mammary cancer development.

ΔN63 suppresses the ability of pregnancy-identified mammary epithelial cells (PIMECs) to drive HER2-positive breast cancer

While pregnancy is known to reduce a woman's life-long risk of breast cancer, clinical data suggest that it can specifically promote HER2 (human EGF receptor 2)-positive breast cancer subtype (HER2+ BC). HER2+ BC, characterized by amplification of HER2, comprises about 20% of all sporadic breast cancers and is more aggressive than hormone receptor-positive breast cancer (the majority of cases). Consistently with human data, pregnancy strongly promotes HER2+ BC in genetic mouse models. One proposed mechanism of this is post-pregnancy accumulation of PIMECs (pregnancy-identified mammary epithelial cells), tumor-initiating cells for HER2+ BC in mice. We previously showed that p63, a homologue of the tumor suppressor p53, is required to maintain the post-pregnancy number of PIMECs and thereby promotes HER2+ BC. Here we set to test whether p63 also affects the intrinsic tumorigenic properties of PIMECs. To this end, we FACS-sorted YFP-labeled PIMECs from p63+/-;ErbB2 and control p63+/+;ErbB2 females and injected their equal amounts into immunodeficient recipients. To our surprise, p63+/- PIMECs showed increased, rather than decreased, tumorigenic capacity in vivo, i.e., significantly accelerated tumor onset and tumor growth, as well as increased self-renewal in mammosphere assays and proliferation in vitro and in vivo. The underlying mechanism of these phenotypes seems to be a specific reduction of the tumor suppressor TAp63 isoform in p63+/- luminal cells, including PIMECs, with concomitant aberrant upregulation of the oncogenic ΔNp63 isoform, as determined by qRT-PCR and scRNA-seq analyses. In addition, scRNA-seq revealed upregulation of several cancer-associated (Il-4/Il-13, Hsf1/HSP), oncogenic (TGFβ, NGF, FGF, MAPK) and self-renewal (Wnt, Notch) pathways in p63+/-;ErbB2 luminal cells and PIMECs per se. Altogether, these data reveal a complex role of p63 in PIMECs and pregnancy-associated HER2+ BC: maintaining the amount of PIMECs while suppressing their intrinsic tumorigenic capacity.

Mismatch repair deficiency predicts response to HER2 blockade in HER2-negative breast cancer

Resistance to endocrine treatment occurs in ~30% of ER+ breast cancer patients resulting in ~40,000 deaths/year in the USA. Preclinical studies strongly implicate activation of growth factor receptor, HER2 in endocrine treatment resistance. However, clinical trials of pan-HER inhibitors in ER+/HER2- patients have disappointed, likely due to a lack of predictive biomarkers. Here we demonstrate that loss of mismatch repair activates HER2 after endocrine treatment in ER+/HER2- breast cancer cells by protecting HER2 from protein trafficking. Additionally, HER2 activation is indispensable for endocrine treatment resistance in MutL- cells. Consequently, inhibiting HER2 restores sensitivity to endocrine treatment. Patient data from multiple clinical datasets supports an association between MutL loss, HER2 upregulation, and sensitivity to HER inhibitors in ER+/HER2- patients. These results provide strong rationale for MutL loss as a first-in-class predictive marker of sensitivity to combinatorial treatment with endocrine intervention and HER inhibitors in endocrine treatment-resistant ER+/HER2- breast cancer patients.

Advances in Rodent Models for Breast Cancer Formation, Progression, and Therapeutic Testing

Breast cancer is a highly complicated disease. Advancement in the treatment and prevention of breast cancer lies in elucidation of the mechanism of carcinogenesis and progression. Rodent models of breast cancer have developed into premier tools for investigating the mechanisms and genetic pathways in breast cancer progression and metastasis and for developing and evaluating clinical therapeutics. Every rodent model has advantages and disadvantages, and the selection of appropriate rodent models with which to investigate breast cancer is a key decision in research. Design of a suitable rodent model for a specific research purpose is based on the integration of the advantages and disadvantages of different models. Our purpose in writing this review is to elaborate on various rodent models for breast cancer formation, progression, and therapeutic testing.

Risk factors of breast cancer among patients in a tertiary care hospitals in Afghanistan: a case control study

Background

Breast cancer is the second most common causes of women’s death, worldwide. Data on risk factors associated with female breast cancer in the Afghan population is very limited. The aim of our study was to identifying risk factor associated with female breast cancer in Afghanistan.

Methods

A retrospective case-control study was conducted with inclusion of 201 cases and 201 controls. Patient information was collected by interviewing the patient through a structured questionnaire. Histopathological information was collected from the hospital integrated laboratory management system. The data was analyzed by using logistic regression with univariate and multivariable analyses to determine the association between breast cancer and predictors.

Results

The results of the current study showed that factors such as: age (OR = 1.02; 95%CI: 0.99–1.04; p-0.148); age at menarche (OR = 0.83; 95%CI: 0.72–0.92; p-0.008); age at first baby (OR = 1.14; 95%CI: 1.07–1.20; p- < 0.001); illiteracy (OR = 1.93; 95%CI: 1.16–3.22; p-0.011); smoking (OR = 2.01; 95%CI: 1.01–3.99; p-0.04) and family history of cancer (OR = 1.98; 95%CI: 1.18–3.32; p-0.009) were significantly associated with breast cancer. However, our study did not demonstrate any statistically significant correlation between breast cancer and some of the predictors that were previously highlighted in literature, such as: marital status, Body Mass Index (BMI), use of hormonal contraceptive, breastfeeding and exercise.

Conclusion

Our study demonstrated that age at menarche, and age at first baby birth, illiteracy, smoking and family history of cancer were significant risk factors associated with development of breast cancer among women in Afghanistan. Health education of women regarding aforementioned predisposing factors are therefore, expected to be valuable in decreasing the burden of breast cancer with reduction of its burden on the healthcare system in Afghanistan.

Breast Cancer During Pregnancy: A Marked Propensity to Triple-Negative Phenotype

Breast and cervical cancers comprise 50% of all cancers during pregnancy. In particular, gestational breast cancer is considered one of the most aggressive types of cancers, which is a rare but fatal disease. However, the incidence of this type of cancer is increasing over the years and its prevalence is expected to rise further as more women delay childbearing. Breast cancer occurring after pregnancy is generally triple negative with specific characterizations of a poorer prognosis and outcome. On the other hand, it has been pointed out that this cancer is associated with a specific group of genes which can be used as precise targets to manage this deadly disease. Indeed, combination therapies consisting of gene-based agents with other cancer therapeutics is presently under consideration. We herein review recent progress in understanding the development of breast cancer during pregnancy and their unique subtype of triple negative which is the hallmark of this type of breast cancer.

Intraductal Injection of Lentivirus Vectors for Stably Introducing Genes into Rat Mammary Epithelial Cells in Vivo

Various retroviral and lentiviral vectors have been used for up-the-teat intraductal injection to deliver markers, oncogenes, and other genes into mammary epithelial cells in mice. These methods along with the large number of genetically engineered mouse lines have greatly helped us learn normal breast development and tumorigenesis. Rats are also valuable models for studying human breast development and cancer. However, genetically engineered rats are still uncommon, and previous reports of intraductal injection of retroviral vectors into rats appear to be inefficient in generating mammary tumors. Here, we report, and describe the method for, stably introducing marker genes and oncogenes into mammary glands in rats using intraductal injection of commonly used lentiviral vectors. This method can infect mammary epithelial cells efficiently, and the infected cells can initiate tumorigenesis, including estrogen receptor-positive and hormone-dependent tumors, which are the most common subtype of human breast cancer but are yet still difficult to model in mice. This technique provides another tool for studying formation, prevention, and treatment of breast cancer, especially estrogen receptor-positive breast cancer.

MiR-920 and LSP1 co-regulate the growth and migration of glioblastoma cells by modulation of JAK2/STAT5 pathway

This study probes the function and mechanism of lymphocyte-specific protein 1 (LSP1) in glioblastoma pathogenesis. According to the data acquired from TCGA, Oncomine and GEO databases, the expression and prognostic value of LSP1 and miR-920 in glioblastoma patients were analyzed. The expression levels of LSP1 in U251 and A172 cell lines were analyzed by qRT-PCR and western blotting. CCK8, colony formation and transwell assays were utilized to test glioblastoma cell malignant abilities. Furthermore, the associations between LSP1 and miR-920 were indentified by bioinformatics analysis and rescue assays. Moreover, the protein expression levels of p-JAK2, JAK2, p-STAT5 and STAT5, as the hallmark of JAK/STAT5 signaling, were detected by western blotting. The observations showed that LSP1 was highly augmented in glioblastoma samples. Additionally, up-regulation of LSP1 was associated with a unfavorable prognosis in glioblastoma patients. Biological experiments revealed that depletion of LSP1 significantly suppressed the proliferation, invasion and migration of U251 and A172 cells. MiR-920, as an upstream regulator of LSP1, negatively modulated LSP1 expression and promoted U251 cells malignant behaviors after miR-920 inhibitor treatment. However, together knockdown LSP1 and miR-920 inhibited these effects. Moreover, the expression levels of p-JAK2 and p-STAT5 were increased or decreased in U251 cells after transfection of miR-920 inhibitor or si-LPS1. Taken together, miR-920 might blocked the malignant development of glioblastoma cells, which is possibly realized by targeting LSP1 and modulation of JAK/STAT5 pathway. These findings implied that miR-920/LSP1 was a potential therapeutic target for glioblastoma treatment.

Pregnancy and Breast Cancer: Pathways to Understand Risk and Prevention

Several studies have made strong efforts to understand how age and parity modulate the risk of breast cancer. A holistic understanding of the dynamic regulation of the morphological, cellular, and molecular milieu of the mammary gland offers insights into the drivers of breast cancer development as well as into potential prophylactic interventions, the latter being a longstanding ambition of the research and clinical community aspiring to eradicate the disease. In this review we discuss mechanisms that react to pregnancy signals, and we delineate the nuances of pregnancy-associated dynamism that contribute towards either breast cancer development or prevention. Further definition of the molecular basis of parity and breast cancer risk may allow the elaboration of tools to predict and survey those who are at risk of breast cancer development.

Mammary stem cells and progenitors: targeting the roots of breast cancer for prevention

Breast cancer prevention is daunting, yet not an unsurmountable goal. Mammary stem and progenitors have been proposed as the cells-of-origin in breast cancer. Here, we present the concept of limiting these breast cancer precursors as a risk reduction approach in high-risk women. A wealth of information now exists for phenotypic and functional characterization of mammary stem and progenitor cells in mouse and human. Recent work has also revealed the hormonal regulation of stem/progenitor dynamics as well as intrinsic lineage distinctions between mammary epithelial populations. Leveraging these insights, molecular marker-guided chemoprevention is an achievable reality.

Combined Inhibition of STAT3 and DNA Repair in Palbociclib-Resistant ER-Positive Breast Cancer

PURPOSE

Cyclin-dependent kinase 4/6 (CDK4/6) inhibitors are currently used in combination with endocrine therapy to treat advanced hormone receptor-positive, HER2-negative breast cancer. Although this treatment doubles time to progression compared with endocrine therapy alone, about 25%-35% of patients do not respond, and almost all patients eventually acquire resistance. Discerning the mechanisms of resistance to CDK4/6 inhibition is crucial in devising alternative treatment strategies.

EXPERIMENTAL DESIGN

Palbociclib-resistant cells (MCF-7 and T47D) were generated in a step-wise dose-escalading fashion. Whole-exome sequencing, genome-wide expression analysis, and proteomic analysis were performed in both resistant and parental (sensitive) cells. Pathway alteration was assessed mechanistically and pharmacologically. Biomarkers of altered pathways were examined in tumor samples from patients with palbociclib-treated breast cancer whose disease progressed while on treatment.

RESULTS

Palbociclib-resistant cells are cross-resistant to other CDK4/6 inhibitors and are also resistant to endocrine therapy (estrogen receptor downregulation). IL6/STAT3 pathway is induced, whereas DNA repair and estrogen receptor pathways are downregulated in the resistant cells. Combined inhibition of STAT3 and PARP significantly increased cell death in the resistant cells. Matched tumor samples from patients with breast cancer who progressed on palbociclib were examined for deregulation of estrogen receptor, DNA repair, and IL6/STAT3 signaling, and results revealed that these pathways are all altered as compared with the pretreatment tumor samples.

CONCLUSIONS

Palbociclib resistance induces endocrine resistance, estrogen receptor downregulation, and alteration of IL6/STAT3 and DNA damage response pathways in cell lines and patient samples. Targeting IL6/STAT3 activity and DNA repair deficiency using a specific STAT3 inhibitor combined with a PARP inhibitor could effectively treat acquired resistance to palbociclib.

Mammary Precancerous Stem and Non-Stem Cells Evolve into Cancers of Distinct Subtypes

There are distinct cell subpopulations in normal epithelial tissue, including stem cells, progenitor cells, and more differentiated cells, all of which have been extensively studied for their susceptibility to tumorigenesis. However, normal cells usually have to progress through a precancerous lesion state before becoming a full-blown tumor. Precancerous early lesions are heterogeneous, and the cell subset that is the primary source of the eventual tumor remains largely unknown. By using mouse models that are tailored to address this question, we identified a keratin 6a-expressing precancerous stem cell (PcSC) subset and a more differentiated whey acidic protein-positive (WAP+) cell subset in mammary precancerous lesions initiated by the Wnt1 oncogene. Both cell subsets rapidly progressed to cancer upon introduction of constitutively active versions of either HRAS or BRAF. However, the resulting tumors were dramatically different in protein profiles and histopathology: keratin 6a+ precancerous cells gave rise to adenocarcinoma, whereas WAP+ cells yielded metaplastic carcinoma with severe squamous differentiation and more robust activation of MEK/ERK signaling. Therefore, both stem and non-stem cells in mammary precancerous lesions can contribute to the eventual cancers, but their differentiation status determines the resulting cancer phenotype. This work identifies a previously unknown player in cancer heterogeneity and suggests that cancer prevention should target precancerous cells broadly and not be limited to PcSC. SIGNIFICANCE: This work uses a novel mouse mammary gland cancer model to show that tumors initiated from different precancerous mammary epithelial cells are distinct.

Hyperprolactinemia-inducing antipsychotics increase breast cancer risk by activating JAK-STAT5 in precancerous lesions

BACKGROUND

Psychiatric medications are widely prescribed in the USA. Many antipsychotics cause serum hyperprolactinemia as an adverse side effect; prolactin-Janus kinase 2 (JAK2)-signal transducer and activator of transcription 5 (STAT5) signaling both induces cell differentiation and suppresses apoptosis. It is controversial whether these antipsychotics increase breast cancer risk.

METHODS

We investigated the impact of several antipsychotics on mammary tumorigenesis initiated by retrovirus-mediated delivery of either ErbB2 or HRas or by transgenic expression of Wnt-1.

RESULTS

We found that the two hyperprolactinemia-inducing antipsychotics, risperidone and pimozide, prompted precancerous lesions to progress to cancer while aripiprazole, which did not cause hyperprolactinemia, did not. We observed that risperidone and pimozide (but not aripiprazole) caused precancerous cells to activate STAT5 and suppress apoptosis while exerting no impact on proliferation. Importantly, we demonstrated that these effects of antipsychotics on early lesions required the STAT5 gene function. Furthermore, we showed that only two-week treatment of mice with ruxolitinib, a JAK1/2 inhibitor, blocked STAT5 activation, restored apoptosis, and prevented early lesion progression.

CONCLUSIONS

Hyperprolactinemia-inducing antipsychotics instigate precancerous cells to progress to cancer via JAK/STAT5 to suppress the apoptosis anticancer barrier, and these cancer-promoting effects can be prevented by prophylactic anti-JAK/STAT5 treatment. This preclinical work exposes a potential breast cancer risk from hyperprolactinemia-inducing antipsychotics in certain patients and suggests a chemoprevention regime that is relatively easy to implement compared to the standard 5-year anti-estrogenic treatment in women who have or likely have already developed precancerous lesions while also requiring hyperprolactinemia-inducing antipsychotics.

Lactation opposes pappalysin-1-driven pregnancy-associated breast cancer

Pregnancy is associated with a transient increase in risk for breast cancer. However, the mechanism underlying pregnancy‐associated breast cancer (PABC) is poorly understood. Here, we identify the protease pappalysin‐1 (PAPP‐A) as a pregnancy‐dependent oncogene. Transgenic expression of PAPP‐A in the mouse mammary gland during pregnancy and involution promotes the deposition of collagen. We demonstrate that collagen facilitates the proteolysis of IGFBP‐4 and IGFBP‐5 by PAPP‐A, resulting in increased proliferative signaling during gestation and a delayed involution. However, while studying the effect of lactation, we found that although PAPP‐A transgenic mice lactating for an extended period of time do not develop mammary tumors, those that lactate for a short period develop mammary tumors characterized by a tumor‐associated collagen signature (TACS‐3). Mechanistically, we found that the protective effect of lactation is associated with the expression of inhibitors of PAPP‐A, STC1, and STC2. Collectively, these results identify PAPP‐A as a pregnancy‐dependent oncogene while also showing that extended lactation is protective against PAPP‐A‐mediated carcinogenesis. Our results offer the first mechanism that explains the link between breast cancer, pregnancy, and breastfeeding.

Crosstalk between STAT5 activation and PI3K/AKT functions in normal and transformed mammary epithelial cells

Janus kinases (JAKs) and signal transducers and activators of transcription (STATs) have been shown to function downstream of several peptide hormones and cytokines that are required for postnatal development and secretory function of the mammary gland. As part of an extended network, these signal transducers can engage in crosstalk with other pathways to facilitate synergistic, and sometimes antagonistic, actions of different growth factors. Specifically, signaling through the JAK2/STAT5 cascade has been demonstrated to be indispensable for the specification, proliferation, differentiation, and survival of secretory mammary epithelial cells. Following a concise description of major cellular programs in mammary gland development and the role of growth factors that rely on JAK/STAT signaling to orchestrate these programs, this review highlights the significance of active STAT5 and its crosstalk with the PI3 kinase and AKT1 for mediating the proliferation of alveolar progenitors and survival of their functionally differentiated descendants in the mammary gland. Based on its ability to provide self-sufficiency in growth signals that are also capable of overriding intrinsic cell death programs, persistently active STAT5 can serve as a potent oncoprotein that contributes to the genesis of breast cancer. Recent experimental evidence demonstrated that, similar to normal developmental programs, oncogenic functions of STAT5 rely on molecular crosstalk with PI3K/AKT signaling for the initiation, and in some instances the progression, of breast cancer. The multitude by which STATs can interact with individual mediators of the PI3K/AKT signaling cascade may provide novel avenues for targeting signaling nodes within molecular networks that are crucial for the survival of cancer cells.

Loss of MutL Disrupts CHK2-Dependent Cell-Cycle Control through CDK4/6 to Promote Intrinsic Endocrine Therapy Resistance in Primary Breast Cancer

Significant endocrine therapy-resistant tumor proliferation is present in ≥20% of estrogen receptor-positive (ER⁺) primary breast cancers and is associated with disease recurrence and death. Here, we uncover a link between intrinsic endocrine therapy resistance and dysregulation of the MutL mismatch repair (MMR) complex (MLH1/3, PMS1/2), and demonstrate a direct role for MutL complex loss in resistance to all classes of endocrine therapy. We find that MutL deficiency in ER⁺ breast cancer abrogates CHK2-mediated inhibition of CDK4, a prerequisite for endocrine therapy responsiveness. Consequently, CDK4/6 inhibitors (CDK4/6i) remain effective in MutL-defective ER⁺ breast cancer cells. These observations are supported by data from a clinical trial where a CDK4/6i was found to strongly inhibit aromatase inhibitor-resistant proliferation of MutL-defective tumors. These data suggest that diagnostic markers of MutL deficiency could be used to direct adjuvant CDK4/6i to a population of patients with breast cancer who exhibit marked resistance to the current standard of care.Significance: MutL deficiency in a subset of ER⁺ primary tumors explains why CDK4/6 inhibition is effective against some de novo endocrine therapy-resistant tumors. Therefore, markers of MutL dysregulation could guide CDK4/6 inhibitor use in the adjuvant setting, where the risk benefit ratio for untargeted therapeutic intervention is narrow. Cancer Discov; 7(10); 1168-83. ©2017 AACR.This article is highlighted in the In This Issue feature, p. 1047.

A Versatile Gene Delivery System for Efficient and Tumor Specific Gene Manipulation in vivo

The Replication-Competent Avian Sarcoma-leukosis virus long-terminal repeat with splice acceptor (RCAS)-Tumor Virus A (TVA) gene delivery system has been created based on the fact that avian sarcoma leukosis virus subgroup A only infects cells expressing its receptor, TVA. This system has been successfully applied to create various mouse models for human cancers. Here we briefly discuss the advantages and the potential caveats of using this RCAS-TVA gene delivery system in cancer research. We also introduce and discuss how our newly designed RCAS-based gene delivery system (RCI-Oncogene, for RCAS-Cre-IRES-Oncogene) allows concise and efficient manipulation of gene expression in tumors in vivo, and how this system can be used to rapidly study the biological function of gene(s) and/or the collaborative actions of multiple genes in regulating tumor initiation, progression and/or metastasis.

Potential of breastmilk analysis to inform early events in breast carcinogenesis: rationale and considerations

This review summarizes methods related to the study of human breastmilk in etiologic and biomarkers research. Despite the importance of reproductive factors in breast carcinogenesis, factors that act early in life are difficult to study because young women rarely require breast imaging or biopsy, and analysis of critical circulating factors (e.g., hormones) is often complicated by the requirement to accurately account for menstrual cycle date. Accordingly, novel approaches are needed to understand how events such as pregnancy, breastfeeding, weaning, and post-weaning breast remodeling influence breast cancer risk. Analysis of breastmilk offers opportunities to understand mechanisms related to carcinogenesis in the breast, and to identify risk markers that may inform efforts to identify high-risk women early in the carcinogenic process. In addition, analysis of breastmilk could have value in early detection or diagnosis of breast cancer. In this article, we describe the potential for using breastmilk to characterize the microenvironment of the lactating breast with the goal of advancing research on risk assessment, prevention, and detection of breast cancer.

Inflammatory breast cancer: unique biological and therapeutic considerations

Through the concerted efforts of many patients, health-care providers, legislators, and other supporters, the past decade has seen the development of the first clinics dedicated to the care of patients with inflammatory breast cancer in the USA and other countries. Together with social networking, advocacy, and education, a few specialised centres have had substantial increases in patient numbers (in some cases ten times higher), which has further expanded the community of science and advocacy and increased the understanding of the disease process. Although inflammatory breast cancer is considered rare, constituting only 2-4% of breast cancer cases, poor prognosis means that patients with the disease account for roughly 10% of breast cancer mortality annually in the USA. I propose that the unique presentation of inflammatory breast cancer might require specific, identifiable changes in the breast parenchyma that occur before the tumour-initiating event. This would make the breast tissue itself a tumour-promoting medium that should be treated as a component of the pathology in multidisciplinary treatment and should be further studied for complementary targets to inhibit the pathobiology that is specific to inflammatory breast cancer.

The PR status of the originating cell of ER/PR-negative mouse mammary tumors

Progesterone receptor (PR) is usually co-localized with estrogen receptor (ER) in normal mammary cells. It is not known whether ER/PR-negative human breast cancer arises from an ER/PR-negative cell or from an ER/PR-positive cell that later lost ER/PR. Using intraductal injection of a lentivirus to deliver both an oncogene (ErbB2) and a floxed green fluorescent protein (GFP) in PR(Cre/+)mice, whose Cre gene is under the control of the PR promoter, we were able to trace the PR status of the infected cells as they progressed to cancer. We found that the resulting early lesions stained negative for PR in most of the cells and usually retained GFP. The resulting tumors lacked ER and PR, and 75% (15/20) of them retained the GFP signal in all tumor cells, suggesting PR was never expressed throughout the evolution of a majority of these tumors. In conclusion, our data demonstrate that ErbB2-initiated ER/PR-negative mammary tumors primarily originate from the subset of the mammary epithelium that is negative for PR and probably ER as well. These findings also provide an explanation for why antihormonal therapy fails to prevent ER-negative breast cancers.

The Status of STAT3 and STAT5 in Human Breast Atypical Ductal Hyperplasia

Signal Transducer and Activation of Transcription factors (STAT3 and STAT5) play important roles in breast epithelial cell differentiation, proliferation, and apoptosis. They have been investigated extensively in established breast cancer, but their activation status in precancerous lesions has not been reported. Formalin-fixed, paraffin-embedded archival tissues from 59 cases of atypical ductal hyperplasia (ADH) and 31 cases of normal human breast tissue as well as 21 cases of usual ductal hyperplasias (UDH) were obtained from the First Hospital of Jilin University, China, and stained for pSTAT3 and pSTAT5 by immunohistochemistry. The median percentage of pSTAT5+ cells in ADH was 12%, not significantly deviant from that in normal breast. The median percentage of pSTAT3+ cells in ADH was 30%, significantly higher than that of normal breast. pSTAT3 and pSTAT5 were exclusive of each other—they were detected in different ADHs or in different cells within the same ADHs. In addition, both pSTAT3 and pSTAT5 were produced in similar percentages of cells in ADHs from cancer-free patients vs. ADHs that were adjacent to an invasive cancer. Our finding of a complementary expression pattern of pSTAT3 and pSTAT5 in ADH suggests that these two transcription factors may have feedback inhibitory effects on each other during early stages of breast cancer evolution, and that disruption of this inverse relationship may be important in the progression from early lesions to cancer, which exhibits positive association between pSTAT3 and pSTAT5.

A Long-Lived Luminal Subpopulation Enriched with Alveolar Progenitors Serves as Cellular Origin of Heterogeneous Mammary Tumors

It has been shown that the mammary luminal lineage could be maintained by luminal stem cells or long-lived progenitors, but their identity and role in breast cancer remain largely elusive. By lineage analysis using Wap-Cre mice, we found that, in nulliparous females, mammary epithelial cells (MECs) genetically marked by Wap-Cre represented a subpopulation of CD61+ luminal progenitors independent of ovarian hormones for their maintenance. Using a pulse-chase lineage-tracing approach based on Wap-Cre adenovirus (Ad-Wap-Cre), we found that Ad-Wap-Cre-marked nulliparous MECs were enriched with CD61+ alveolar progenitors (APs) that gave rise to CD61- alveolar luminal cells during pregnancy/lactation and could maintain themselves long term. When transformed by different oncogenes, they could serve as cells of origin of heterogeneous mammary tumors. Thus, our study revealed a type of long-lived AP within the luminal lineage that may serve as the cellular origin of multiple breast cancer subtypes.

Luminal epithelial cells within the mammary gland can produce basal cells upon oncogenic stress

In the normal mammary gland, the basal epithelium is known to be bipotent and can generate either basal or luminal cells, whereas the luminal epithelium has not been demonstrated to contribute to the basal compartment in an intact and normally developed mammary gland. It is not clear whether cellular heterogeneity within a breast tumor results from transformation of bipotent basal cells or from transformation and subsequent basal conversion of the more differentiated luminal cells. Here we used a retroviral vector to express an oncogene specifically in a small number of the mammary luminal epithelial cells and tested their potential to produce basal cells during tumorigenesis. This in-vivo lineage-tracing work demonstrates that luminal cells are capable of producing basal cells on activation of either polyoma middle T antigen or ErbB2 signaling. These findings reveal the plasticity of the luminal compartment during tumorigenesis and provide an explanation for cellular heterogeneity within a cancer.

Molecular drivers of lobular carcinoma in situ

Lobular carcinoma in situ (LCIS) is considered to be a risk factor for the development of invasive breast carcinoma, but it may also be a non-obligate precursor to invasive lobular carcinoma (ILC). Many LCIS lesions do not progress to ILC, and the molecular changes that are necessary for progression from LCIS to ILC are poorly understood. Disruption in the E-cadherin complex is the hallmark of lobular lesions, but other signaling molecules, such as PIK3CA and c-src, are consistently altered in LCIS. This review focuses on the molecular drivers of lobular carcinoma, a more complete understanding of which may give perspective on which LCIS lesions progress, and which will not, thus having immense clinical implications.

Krt6a-positive mammary epithelial progenitors are not at increased vulnerability to tumorigenesis initiated by ErbB2

While most breast cancers are thought to arise from the luminal layer of the breast tissue, it remains unclear which specific cells in the luminal layer are the cells of origin of breast cancer. We have previously reported that WAP-positive luminal epithelial cells are at increased susceptibility to tumor initiation by ErbB2 compared to the bulk population, while the mammary cells with canonical Wnt signaling activity fail to evolve into tumors upon ErbB2 activation. Here, we used retrovirus to introduce ErbB2 into the Krt6a-positive mammary progenitor subset of the luminal epithelium and, for comparison, into the mammary luminal epithelium indiscriminately. Tumors developed from both groups of cells with a similar latency. These data indicate that the Krt6a-positive subset of mammary epithelial cells can be induced to form cancer by ErbB2 but it is not more susceptible to tumorigenesis initiated by ErbB2 than the bulk population of the luminal epithelium.

Risk determination and prevention of breast cancer

Breast cancer is an increasing public health problem. Substantial advances have been made in the treatment of breast cancer, but the introduction of methods to predict women at elevated risk and prevent the disease has been less successful. Here, we summarize recent data on newer approaches to risk prediction, available approaches to prevention, how new approaches may be made, and the difficult problem of using what we already know to prevent breast cancer in populations. During 2012, the Breast Cancer Campaign facilitated a series of workshops, each covering a specialty area of breast cancer to identify gaps in our knowledge. The risk-and-prevention panel involved in this exercise was asked to expand and update its report and review recent relevant peer-reviewed literature. The enlarged position paper presented here highlights the key gaps in risk-and-prevention research that were identified, together with recommendations for action. The panel estimated from the relevant literature that potentially 50% of breast cancer could be prevented in the subgroup of women at high and moderate risk of breast cancer by using current chemoprevention (tamoxifen, raloxifene, exemestane, and anastrozole) and that, in all women, lifestyle measures, including weight control, exercise, and moderating alcohol intake, could reduce breast cancer risk by about 30%. Risk may be estimated by standard models potentially with the addition of, for example, mammographic density and appropriate single-nucleotide polymorphisms. This review expands on four areas: (a) the prediction of breast cancer risk, (b) the evidence for the effectiveness of preventive therapy and lifestyle approaches to prevention, (c) how understanding the biology of the breast may lead to new targets for prevention, and (d) a summary of published guidelines for preventive approaches and measures required for their implementation. We hope that efforts to fill these and other gaps will lead to considerable advances in our efforts to predict risk and prevent breast cancer over the next 10 years.

A p53/ARF-dependent anticancer barrier activates senescence and blocks tumorigenesis without impacting apoptosis

In response to oncogene activation and oncogene-induced aberrant proliferation, mammalian cells activate apoptosis and senescence, usually via the p53-ARF tumor-suppressor pathway. Apoptosis is a known barrier to cancer and is usually downregulated before full malignancy, but senescence as an anticancer barrier is controversial due to its presence in the tumor environment. In addition, senescence may aid cancer progression via releasing senescence-associated factors that instigate neighboring tumor cells. Here, it is demonstrated that apoptosis unexpectedly remains robust in ErbB2 (ERBB2/HER2)-initiated mammary early lesions arising in adult mice null for either p53 or ARF. These early lesions, however, downregulate senescence significantly. This diminished senescence response is associated with accelerated progression to cancer in ARF-null mice compared with ARF-wild-type mice. Thus, the ARF-p53 pathway is dispensable for the apoptosis anticancer barrier in the initiation of ErbB2 breast cancer, the apoptosis barrier alone cannot halt mammary tumorigenesis, and senescence is a key barrier against carcinogenesis.

IMPLICATIONS

Findings in this relevant mouse model of HER2-driven breast cancer suggest that effective prevention relies upon preserving both ARF/p53-independent apoptosis and ARF/p53-dependent senescence.

Genome-wide DNA methylation profiling reveals parity-associated hypermethylation of FOXA1

Early pregnancy in women by the age of 20 is known to have a profound effect on reduction of lifelong breast cancer risk as compared to their nulliparous counterparts. Additional pregnancies further enhance the protection against breast cancer development. Nationwide trend of delayed pregnancy may contribute to the recently reported increase in the incidence of advanced breast cancer among young women in this country. The underlying mechanism for the parity-associated reduction of breast cancer risk is not clearly understood. The purpose of the current study is to use whole-genome DNA methylation profiling to explore a potential association between parity and epigenetic changes in breast tissue from women with early parity and nulliparity. Breast tissue was collected from age-matched cancer-free women with early parity (age < 20; n = 15) or nulliparity (n = 13). The methyl-CpG binding domain-based capture-sequencing technology was used for whole-genome DNA methylation profiling. Potential parity-associated hypermethylated genes were further verified by locus-specific pyrosequencing, using an expanded cohort of parous (n = 19) and nulliparous (n = 16) women that included the initial samples used in the global analysis. Our study identified six genes that are hypermethylated in the parous group (P < 0.05). Pyrosequencing confirmed parity-associated hypermethylation at multiple CpG islands of the FOXA1 gene, which encodes a pioneer factor that facilitates chromatin binding of estrogen receptor α. Our work identifies several potential methylation biomarkers for parity-associated breast cancer risk assessment. In addition, the results are consistent with the notion that parity-associated epigenetic silencing of FOXA1 contributes to long-term attenuation of the estrogenic impact on breast cancer development.

Targeting the link between late pregnancy and breast cancer

Why does a first pregnancy after age 35 increase the risk of breast cancer, and what can be done to combat this?